[aspect-devel] A question for setting the depth-dependent viscosity (Wolfgang Bangerth)

[Max Rudolph]

> Date: Mon, 11 Jan 2016 07:36:44 -0600
> From: Wolfgang Bangerth <bangerth at tamu.edu>
> To: Nan.Zhang at Colorado.EDU, "aspect-devel at geodynamics.org"
>         <aspect-devel at geodynamics.org>
> Subject: Re: [aspect-devel] A question for setting the depth-dependent
>         viscosity
> Message-ID: <5693AFEC.9050701 at tamu.edu>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
> On 01/11/2016 05:54 AM, Nan Zhang wrote:
> >
> > (1) I try to find a material model option having both depth-,
> > temperature-dependent viscosity and composition field. Is there an
> existing
> > "material model" for this?
>
> I must admit that I don't know -- there are too many by now. You need to go
> through the list of models that are available.
>
>
> > (2) after I get the right "material model" option, I wonder what is the
> exact
> > syntax in the input file for my formulation
> enta(r,T)=enta0(r)*exp[E(0.5-T)]?
>
> The factor exp[E(0.5-T)] needs to come from the underlying material model.
> For
> ent0, you should be able to use something of the form
>
>    if(sqrt(x*x+y*y+z*z)<5000, 1.5, 0.5)
>
> or whatever values you need.
>

The "depth dependent" material model gets depth directly, so there's no
need to calculate the radius in this manner:

  subsection Depth dependent model
    set Base model = simple
    set Depth dependence method = Function
    subsection Viscosity depth function
      set Variable names = d
      set Function expression = if(d>6.70e5,3.0e22,1.0e21);
    end
  end


If you prefer to use a file that specifies the depth-dependent prefactor,
take a look at these files:
https://github.com/geodynamics/aspect/blob/master/tests/depth_dependent_box_file_simple.prm
https://github.com/geodynamics/aspect/blob/master/tests/visc_depth.txt

If you read the prefactor from a file, the prefactor is interpolated
(linearly), whereas if you provide the prefactor using a list of depths and
prefactors, the prefactor is piecewise constant and each depth provided
specifies the bottom of a layer. In retrospect, we could have added an
option to specify the interpolation method for each case.
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